Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 551: Which of the following statements is NOT true about poliomyelitis?

A. Subclinical cases are more common.
B. Less than 1% of infected cases will show paralysis.
C. Poliomyelitis can be transmitted by nasal discharge. (Correct Answer)
D. Type 1 poliovirus causes epidemics more commonly.

Explanation: **Explanation** The correct answer is **C**. While poliovirus is an enterovirus, its primary mode of transmission is the **fecal-oral route**. In the early stages of infection, the virus is present in the pharynx, but it is excreted in stools for several weeks. Crucially, **nasal discharge is not a significant source of infection**, and the virus is not transmitted via respiratory droplets or nasal secretions in a way that contributes to its epidemiology. **Analysis of other options:** * **Option A (Subclinical cases):** This is true. In polio, the vast majority of infections are asymptomatic or mild. For every 1 paralytic case, there are roughly 100–1000 subclinical cases (the "Iceberg Phenomenon"). * **Option B (Paralysis rate):** This is true. Paralytic poliomyelitis occurs in **less than 1%** of all infections. Most cases are either subclinical, abortive (minor illness), or non-paralytic aseptic meningitis. * **Option D (Type 1 virus):** This is true. Historically, **Type 1** is the most common cause of epidemics and is responsible for most cases of paralytic polio. Type 2 and Type 3 are less frequently associated with large-scale outbreaks. **High-Yield Clinical Pearls for NEET-PG:** * **Reservoir:** Man is the only reservoir; there are no chronic carriers. * **Infectivity:** Maximum infectivity occurs during the late incubation period and the first week of clinical illness. * **Virus Types:** Type 1 (Epidemogenic), Type 2 (Eradicated globally in 2015), Type 3 (Eradicated globally in 2019). * **Immunity:** Infection with one type does not provide cross-immunity against other types.

Question 552: Who introduced the germ theory of disease?

A. Robert Koch
B. Loeffler
C. Walter Reed
D. John Snow (Correct Answer)

Explanation: **Explanation:** The correct answer is **John Snow**. While the term "Germ Theory" is often associated with later microbiological discoveries, John Snow is credited with introducing the fundamental concept through his epidemiological work during the 1854 Broad Street cholera outbreak. He proposed that cholera was caused by a specific particulate "poison" transmitted via contaminated water, effectively challenging the then-dominant "Miasma Theory" (disease caused by bad air). His systematic approach earned him the title of the **"Father of Modern Epidemiology."** **Analysis of Incorrect Options:** * **Robert Koch (Option A):** He provided the definitive scientific proof for germ theory by identifying the specific causative agents for Anthrax, Tuberculosis, and Cholera. He formulated **Koch’s Postulates**, which are the gold standard for linking a microbe to a disease. * **Loeffler (Option B):** Friedrich Loeffler was a disciple of Koch who identified the organism causing Diphtheria (*Corynebacterium diphtheriae*). * **Walter Reed (Option C):** A U.S. Army physician who proved that Yellow Fever is transmitted by mosquitoes (*Aedes aegypti*), rather than by direct contact. **High-Yield Clinical Pearls for NEET-PG:** * **Louis Pasteur:** Often called the "Father of Germ Theory" in a laboratory context for his work on fermentation and pasteurization. * **John Snow’s "Ghost Map":** His use of spot maps to track cholera cases is a classic example of **Descriptive Epidemiology**. * **Jacob Henle:** He was the first to suggest the germ theory in a formal scientific treatise, which his student Robert Koch later proved. * **Golden Age of Bacteriology:** Spanned from 1875 to 1900, initiated by the works of Pasteur and Koch.

Question 553: The first case of Severe Acute Respiratory Syndrome (SARS) was reported in:

A. 1999
B. 2000
C. 2001
D. 2002 (Correct Answer)

Explanation: **Explanation:** **Correct Answer: D. 2002** The first case of **Severe Acute Respiratory Syndrome (SARS)**, caused by the SARS-associated coronavirus (SARS-CoV), was identified in **November 2002**. The outbreak originated in the Guangdong Province of China. It was the first major new infectious disease of the 21st century to exhibit significant international spread, eventually affecting over 26 countries. The WHO issued a global alert in March 2003, but the index case (patient zero) is epidemiologically traced back to late 2002. **Analysis of Incorrect Options:** * **A, B, and C (1999, 2000, 2001):** During these years, there were no documented cases of SARS. While other respiratory pathogens were circulating, the specific mutation and zoonotic spillover (from civet cats/bats to humans) that created SARS-CoV had not yet occurred or been detected in the human population. **High-Yield Clinical Pearls for NEET-PG:** * **Causative Agent:** SARS-CoV (a lineage B betacoronavirus). * **Reservoir:** Horseshoe bats are the natural reservoir; Civet cats acted as the intermediate host. * **Transmission:** Primarily through respiratory droplets and fomites. * **Clinical Feature:** Characterized by high fever, malaise, and progressive respiratory failure. Unlike COVID-19, peak viral shedding occurred during the second week of illness, making hospital-based transmission (nosocomial) a major feature. * **Case Fatality Rate (CFR):** Approximately 10%. * **Status:** No cases of SARS have been reported worldwide since 2004.

Question 554: A study was conducted to assess the role of radiation in leukemia. Among 100 patients with leukemia, 70 reported a history of radiation exposure. Among 100 controls, 30 reported a history of radiation exposure. What type of bias is most likely present in this study?

A. Reporting bias
B. Recall bias (Correct Answer)
C. Interviewer bias
D. Hawthorne bias

Explanation: ### Explanation **1. Why Recall Bias is the Correct Answer:** The study described is a **Case-Control Study** (starting with diseased individuals/cases and comparing them to healthy controls). In such studies, participants are asked to remember past exposures. **Recall bias** occurs when there is a systematic difference in the accuracy or completeness of memories between cases and controls. Patients with a serious disease (Leukemia) are more likely to ruminate on their past and "search their memory" for potential causes, leading them to remember or even over-report exposure to radiation. Conversely, healthy controls have no such motivation and may under-report or forget similar exposures. This differential recall leads to an overestimation of the association between the exposure and the disease. **2. Analysis of Incorrect Options:** * **Reporting Bias (A):** This occurs when a participant consciously chooses not to disclose information (e.g., due to social stigma or legal concerns). It is a "selective revealing" rather than a memory failure. * **Interviewer Bias (C):** This occurs when the researcher/interviewer influences the results, often by probing cases more intensely than controls because they know the hypothesis. While possible here, the question focuses on the *subjects'* reporting of history. * **Hawthorne Bias (D):** This is the tendency of study participants to change their behavior because they know they are being observed. It is typically seen in prospective cohort studies or trials, not retrospective case-controls. **3. NEET-PG Clinical Pearls:** * **Case-Control Studies** are most prone to **Recall Bias**. * **Cohort Studies** are most prone to **Selection Bias** and **Loss to follow-up (Attrition bias)**. * **To minimize Recall Bias:** Use objective records (medical files) instead of interviews, or use "Blinded" participants and standardized questionnaires. * **Neyman Bias (Prevalence-incidence bias):** Occurs when cases are selected from survivors (prevalent cases) rather than new (incident) cases.

Question 555: In epidemiology, spot maps are used for the depiction of which aspect of a disease?

A. Local distributions (Correct Answer)
B. Rural-urban variations
C. National variations
D. International variations

Explanation: **Explanation:** **Spot maps** are a fundamental tool in descriptive epidemiology used to represent the **geographic distribution** of cases. The correct answer is **Local distributions** because spot maps plot individual cases (represented by dots or symbols) on a map of a specific, limited area such as a neighborhood, village, or city block. * **Why it is correct:** By pinpointing the exact location of cases, spot maps help identify **clusters** or "hotspots." This allows epidemiologists to hypothesize about a common source of infection. A classic historical example is John Snow’s 1854 map of cholera cases in London, which identified the Broad Street pump as the source. * **Why other options are incorrect:** * **Rural-urban, National, and International variations:** These represent large-scale geographical comparisons. For these levels, **Choropleth maps** (shaded maps showing density or rates) are used rather than spot maps. Spot maps become cluttered and lose utility when applied to large populations or vast geographic areas. **High-Yield NEET-PG Pearls:** 1. **Spot Map Limitation:** It shows the **absolute number** of cases but does not account for the population at risk (denominator). Therefore, it cannot be used to calculate the **incidence rate** or assess the risk of disease in an area. 2. **Correlative Map:** If a spot map shows both the cases and the suspected source (e.g., wells, factories), it is sometimes called a correlative map. 3. **Data Type:** Spot maps are used for **Point Source Epidemics** to identify the focus of an outbreak.

Question 556: Which vaccine should not be given during pregnancy?

A. MMR (Correct Answer)
B. Rabies
C. Hepatitis B
D. Diphtheria

Explanation: **Explanation:** The core principle in obstetric immunization is that **Live Attenuated Vaccines** are generally contraindicated during pregnancy. This is due to the theoretical risk of the vaccine virus crossing the placenta and causing fetal infection or congenital anomalies. **1. Why MMR is the correct answer:** The MMR (Measles, Mumps, and Rubella) vaccine contains live attenuated viruses. The Rubella component is particularly concerning as it poses a theoretical risk of **Congenital Rubella Syndrome (CRS)**. Therefore, MMR is strictly contraindicated in pregnancy. Women are advised to avoid pregnancy for at least 28 days (4 weeks) after receiving the MMR vaccine. **2. Why the other options are incorrect:** * **Rabies:** This is a **killed vaccine**. It is administered as post-exposure prophylaxis. Because rabies is 100% fatal, the vaccine is never withheld in pregnancy if an exposure occurs (Life over Limb/Fetus). * **Hepatitis B:** This is a **recombinant/subunit vaccine**. It is safe and indicated for pregnant women at high risk of infection. * **Diphtheria:** Usually given as Tdap or Td (Tetanus and adult Diphtheria), these are **toxoid vaccines**. They are not only safe but recommended during pregnancy to provide passive immunity to the newborn. **High-Yield NEET-PG Pearls:** * **Contraindicated Live Vaccines:** MMR, Varicella, Yellow Fever, Oral Polio (OPV), and BCG. (Note: Yellow Fever may be given if the risk of exposure is unavoidable). * **Safe Vaccines:** All Killed/Inactivated vaccines, Toxoids (Tetanus, Diphtheria), and Recombinant vaccines (Hep B). * **Influenza:** The **Inactivated** Influenza vaccine is highly recommended for all pregnant women during flu season. * **Standard Care:** In India, under the Universal Immunization Programme (UIP), pregnant women receive two doses of **Td** (Tetanus & adult Diphtheria) or a booster.

Question 557: Which of the following do male mosquitoes preferably feed on?

A. Human blood
B. Animal blood
C. Plant juices (Correct Answer)
D. None of the above

Explanation: **Explanation:** The correct answer is **C. Plant juices**. In the field of medical entomology, it is a fundamental concept that **only female mosquitoes bite** and feed on blood. Female mosquitoes require a blood meal (either human or animal) to obtain the necessary proteins and iron required for the development and production of eggs. In contrast, **male mosquitoes do not produce eggs** and therefore have no physiological requirement for blood. Their mouthparts are not designed for piercing skin. Instead, both male and female mosquitoes primarily feed on **plant juices, nectar, and sugar sources** to obtain the energy (carbohydrates) needed for survival and flight. Since males feed exclusively on these sugar sources, "Plant juices" is the correct choice. **Analysis of Incorrect Options:** * **A & B (Human and Animal blood):** These are incorrect because males lack the specialized proboscis required to pierce skin. Blood feeding is a sex-specific behavior reserved for females of medically important genera like *Anopheles*, *Culex*, and *Aedes*. * **D (None of the above):** This is incorrect as plant nectar is the primary nutritional source for male mosquitoes. **High-Yield Facts for NEET-PG:** * **Vector Competence:** Only female mosquitoes act as vectors for diseases such as Malaria, Dengue, Zika, and Filariasis because they are the only ones that practice hematophagy (blood-feeding). * **Life Cycle:** Mosquitoes undergo complete metamorphosis (Egg → Larva → Pupa → Adult). * **Resting Habits:** Knowledge of whether a mosquito is **endophilic** (rests indoors) or **exophilic** (rests outdoors) is crucial for planning Integrated Vector Management (IVM) strategies like Indoor Residual Spraying (IRS). * **Feeding Time:** *Aedes* is typically a day-biter, while *Anopheles* and *Culex* are generally nocturnal or crepuscular (dawn/dusk) biters.

Question 558: What is true about total fertility rate?

A. Average number of children born to a woman during her reproductive period.
B. Average number of daughters born to a mother. (Correct Answer)
C. Magnitude of completed family size.
D. Average number of live births in a year per 100 women.

Explanation: **Explanation** The question asks for the definition of **Total Fertility Rate (TFR)**. In epidemiology and demography, TFR is defined as the average number of children that would be born to a woman if she were to live to the end of her childbearing years and bear children in accordance with current age-specific fertility rates. **Why Option A is Correct:** TFR represents the **average number of children** a woman would have during her entire reproductive span (usually 15–49 years). It is considered the best single indicator of fertility as it is independent of the age structure of the population. **Why Other Options are Incorrect:** * **Option B:** This describes the **Gross Reproduction Rate (GRR)**. GRR is similar to TFR but specifically counts only the number of *daughters* born to a mother, representing the potential for future population replacement. * **Option C:** This refers to **Completed Family Size**, which is a retrospective measure calculated for a cohort of women who have finished their reproductive life. While TFR *estimates* this, it is not the definition. * **Option D:** This is a variation of the **General Fertility Rate (GFR)**, which is the number of live births per 1,000 women in the reproductive age group (15–49 years) in a given year. **High-Yield NEET-PG Pearls:** * **Replacement Level Fertility:** A TFR of **2.1** is considered the replacement level, where a population exactly replaces itself from one generation to the next. * **Current Status:** India’s TFR has recently declined to **2.0** (NFHS-5), which is below the replacement level. * **Net Reproduction Rate (NRR):** If NRR is **1**, it signifies that a mother is being replaced by exactly one daughter (accounting for mortality). This is the demographic goal for population stabilization.

Question 559: Which of the following genera includes the 'tiger mosquito'?

A. Anopheles
B. Mansonia
C. Aedes (Correct Answer)
D. Culex

Explanation: **Explanation:** The correct answer is **C. Aedes**. The **Aedes mosquito** (specifically *Aedes albopictus*) is popularly known as the **'Tiger Mosquito'** due to the characteristic bold, white transverse stripes on its black body and legs. This species, along with *Aedes aegypti*, is a highly efficient vector for several viral diseases. **Why the other options are incorrect:** * **Anopheles:** Known as the vector for **Malaria**. They are typically identified by their spotted wings and the fact that they rest at a 45-degree angle to the surface. * **Mansonia:** These mosquitoes are the primary vectors for **Brugian Filariasis**. They are unique because their larvae attach to the submerged roots of aquatic plants (like *Pistia*) to breathe. * **Culex:** Often called the "nuisance mosquito," it is the vector for **Bancroftian Filariasis** and **Japanese Encephalitis**. They typically breed in dirty, stagnant water. **High-Yield Clinical Pearls for NEET-PG:** 1. **Aedes Characteristics:** They are **"day biters"** (peak activity early morning and evening) and **"container breeders"** (preferring clean, stagnant water in flower pots, tires, or coolers). 2. **Diseases Transmitted:** Dengue (Break-bone fever), Chikungunya, Zika virus, and Yellow Fever. 3. **Flight Range:** Aedes has a very short flight range (usually <100 meters), making localized source reduction the most effective control strategy. 4. **Nervousness:** Aedes is known as a "nervous feeder," often biting multiple people to complete a single blood meal, which leads to rapid outbreaks.

Question 560: Which toxin is responsible for causing endemic ascites?

A. BOAA
B. Pyrrolizidine alkaloids (Correct Answer)
C. Aflatoxin
D. Sanguinarine

Explanation: **Explanation:** **Endemic Ascites** is a clinical condition characterized by sudden onset of ascites and jaundice, primarily caused by **Pyrrolizidine alkaloids**. These toxins are found in the seeds of *Crotalaria* species (commonly known as *Jhunjhunia*). In India, outbreaks have historically occurred in regions like Madhya Pradesh and Chhattisgarh when *Crotalaria* seeds accidentally contaminate staple food crops like Panicum miliare (Gondli). Pathologically, these alkaloids cause **Veno-Occlusive Disease (VOD)** by damaging the endothelium of hepatic venules, leading to post-sinusoidal portal hypertension. **Analysis of Incorrect Options:** * **A. BOAA (Beta-Oxalyl-Amino-Alanine):** This neurotoxin is found in *Lathyrus sativus* (Khesari Dal). It causes **Lathyrism**, a condition characterized by spastic paraplegia, not ascites. * **C. Aflatoxin:** Produced by *Aspergillus flavus* contaminating stored grains (like groundnuts). Chronic exposure is a major risk factor for **Hepatocellular Carcinoma**, while acute toxicity causes toxic hepatitis. * **D. Sanguinarine:** This toxin is found in **Argemone mexicana** (Prickly Poppy) seeds. Contamination of mustard oil with Argemone oil leads to **Epidemic Dropsy**, characterized by bilateral pitting edema, cardiac failure, and glaucoma. **High-Yield Clinical Pearls for NEET-PG:** * **Veno-Occlusive Disease (VOD):** The hallmark of Pyrrolizidine toxicity. * **Epidemic Dropsy vs. Endemic Ascites:** Dropsy presents with limb edema and cardiac signs; Ascites presents with abdominal fluid and hepatomegaly. * **Argemone Test:** Nitric acid test and Paper chromatography are used to detect Sanguinarine. * **Lathyrism Prevention:** Steeping treatment or parboiling of pulses helps remove BOAA.

Practice by Chapter

Principles of Epidemiology

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Measures of Disease Frequency

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Epidemiological Study Designs

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Descriptive Epidemiology

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Analytical Epidemiology

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Experimental Epidemiology

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Screening for Disease

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Surveillance Systems

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Investigation of an Epidemic

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Association and Causation

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Modern Epidemiological Methods

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Critical Appraisal of Epidemiological Studies

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